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Student chips in with new technique for cutting silicon wafers

Leaders for Global Operation internship project earns award, could save millions for company.
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Leaders for Global Operations
Weng Hong Teh (left) shares an award with his internship advisors (l-r) CU Tan of SanDisk and MIT professors Roy Welsch and Duane Boning.
Weng Hong Teh (left) shares an award with his internship advisors (l-r) CU Tan of SanDisk and MIT professors Roy Welsch and Duane Boning.

Weng Hong Teh really chipped in during his Leaders for Global Operations (LGO) internship project at SanDisk Corporation — his work on silicon wafers earned him and his advisors a special award and is already being used in production of SanDisk memory products.

Teh will graduate soon from the MIT LGO program, in which students earn an MBA from the Sloan School of Management plus an MS in one of seven engineering disciplines in two years. The program includes a six-month on-site internship at an LGO partner company where students work on a real-world operations or manufacturing problem. The research and solutions stemming from the internship lead to the dual-degree master's thesis.

During his internship project at one of partner company SanDisk’s test-and-assembly factories in Shanghai, Teh developed a better method for cutting up large round silicon wafers into square microprocessor chips. The chips are as thin as 25 microns, which is one-third to one-fourth the diameter of an average human hair. When the wafers are cut with a saw or even a laser, some of the resulting microprocessors must be discarded because of defects cased by the cutting process — for example, when the edges are not precisely smooth.

Teh's laser technology actually causes controlled cracking from the inside rather than a complete cut from the outside. He calls his method "stealth dicing" because it employs a laser that cuts the wafer from the inside out, rather than straight across in one direction and then again after turning 90 degrees like a waffle. The laser operates at a wavelength that's transparent to the shiny surface of the silicon bulk material, so the laser beam doesn't get absorbed and cause ablation damage to the wafer.

Although the technique had been used previously for other niche industries, Teh adapted it and combined two tandem processes to achieve a novel integration flow he called "p-SDBG" (partial stealth dicing before grinding) that can circumvent the energy-reflection issues that are usually associated with silicon memory wafers. Testing revealed that stealth dicing resulted in an average of 3.5 percent higher yield of defect-free memory chips, potentially saving the company an estimated $12 million a year.

In a blog entry he wrote whole working on his internship in Sept. 2014, Teh noted that he was initially skeptical of how much impact he could make in a relatively short time, but he found he had considerable freedom to define his project due in part to his prior semiconductor experience at Intel. 

"I am an individual contributor, group leader, integrator, supplier manager and everything in between. Sweet!" he wrote. "I dare say that this internship period during MIT LGO likely enabled the most life-changing experience I have had for a while."

Teh, who is earning his MS in electrical enginering and computer science, also has a PhD in physics from Cambridge University and a master's degree in advanced materials from the National University of Singapore.

In appreciation for his efforts, SanDisk gave glass statuettes and memory disk replicas (including one imprinted with Teh's smiling face) to him and his MIT faculty advisors, professor of electrical engineering and computer science Duane S. Boning and professor of statistics and engineering systems Roy Welsch. The trio has submitted papers based on his internship to Applied Physics Letters and two other high-impact factor engineering journals, and Teh presented them at an international SanDisk conference in Nov. 2014.

As if all that weren't enough, he also filed for a patent that grew out of a side project during his internship and did some management education at SanDisk. At the request of K.L. Bock, general manager and vice president for SanDisk Shanghai, he developed and delivered an MBA Leadership Series in which he discussed selected business case studies with the directors of the SanDisk Shanghai site, learning from the best of lessons from the West and the East. His final delivery was based on a case he co-developed with his LGO classmate, Adam Traina, based on Traina's boat-racing experience.

"That was fun," said Teh, who will join SanDisk in Milpitas, California, as director of advanced manufacturing and engineering after he graduates in June.

Teh had high praise for his MIT education ("an MIT strength is problem-solving from first principles," he said) and especially the LGO curriculum. "The leadership literature taught, shared, and discussed is pretty unique to LGO. It facilitates a deliberate experimentation" with different leadership styles and techniques, he said, noting that his classes exposed him for the first time to the thinking of leaders including Martin Luther King Jr. and Burma's Aung San Suu Kyi.

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